Diazolidinyl urea and iodopropynyl butylcarbamate: a synergistic blend.

To improve the effectiveness of imidazolidinyl urea, patented in 1966,[1] we have developed a synergistic blend(a) (US Pat.5,428,050) of diazolidinyl urea (DU), first introduced in 1981,(17) with iodopropynyl butylcarbamate (IPBC) [ILLUSTRATION FOR FIGURE 1-1 OMITTED].[18, 4] DU has been one of the most widely used and fastest growing antimicrobials in the personal-care and pharmaceutical industries; results from a number of scientific studies and reviews by the US Cosmetic Ingredient Review (CIR) board initiated its acceptance by US, European and Asian/Pacific markets during the past decade.[5] IPBC has been used as a fungicide since the 1970s; with its more recent improvements regarding purity, it also has gained increasing use in personal-care formulations. The CIR ruled it safe at concentrations up to 0.10%.[6]

Synergism

Because synergism is a cooperative action of two ingredients so that their total effect is greater than the sum of the two effects taken independently, this chemistry uses the properties of DU and IPBC effectively. A synergistic blend, including that of DU and IPBC, enables a formulator to use reduced levels of two preservatives and still achieve microbiological efficacy. This new preservative combines the advantages of DU and IPBC at a 100:1 ratio. This blend is water soluble at concentrations up to 1.00%, which allows good solubility at the recommended usage levels of 0.05% to 0.20%.

Many combinations of preservatives currently used today may be additive or unwittingly antagonistic in nature. Additivity describes the combined effect of two preservatives that is equal to the sum of the effect of [TABULAR DATA FOR TABLE 1-1 OMITTED] each preservative alone. Antagonistic blends exhibit an interfering action whereby the total effect of the preservatives is less than the sum of the individual effects. That is not to say a blend that is termed antagonistic will not adequately preserve a formulation. Although a synergistic blend exerts a greater effect than the individual components do, the preservative blend must be thoroughly evaluated in a finished formulation to reveal its full potential.

Interactions: The interaction of the components in a blend can be described as either additive, antagonistic or synergistic. If the fractional inhibitory concentration (FIC) of both preservatives in a blend are plotted against one another, the type of blend can be determined from the relationship presented on an isobologram [ILLUSTRATION FOR GRAPH 1-1 OMITTED].[8]

The FIC indicates the inhibition of an organism due to one of the components in a preservative blend. The intercepts of the straight line joining the FICs indicate the minimum inhibitory concentration (MIC) for each preservative. The line itself represents the amount of each preservative in a blend required to achieve the desired endpoint (the MIC). A linear relationship will represent an additive blend because the effect of the blend is due to…